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A255924
Bases b for which exactly three Wieferich primes p with p < b exist such that p is a base-b Wieferich prime.
11
19, 28, 53, 68, 80, 89, 107, 129, 137, 143, 145, 146, 147, 148, 170, 177, 181, 197, 215, 224, 253, 263, 268, 299, 307, 324, 332, 333, 334, 339, 341, 349, 350, 354, 357, 359, 360, 362, 368, 373, 377, 389, 393, 399, 402, 403, 410, 413, 437, 440, 449, 451, 457
OFFSET
1,1
COMMENTS
Numbers b such that A255920(b) = 3.
LINKS
Eric Weisstein's World of Mathematics, Wieferich Prime
PROG
(PARI) is(n) = my(i=0); forprime(p=1, n-1, if(Mod(n, p^2)^(p-1)==1, i++); if(i > 3, return(0))); i==3
(Sage) [b for b in range(3, 458) if len([p for p in range(2, b) if is_prime(p) and mod(b, p^2)^(p-1)==1])==3] # Danny Rorabaugh, Mar 31 2015
CROSSREFS
Cf. A255920.
Cf. bases b with exactly k base-b Wieferich primes less than b: A255921 (k=0), A255922 (k=1), A255923 (k=2), A255925 (k=4), A325881 (k=5), A325882 (k=6), A325883 (k=7), A325884 (k=8), A325885 (k=9), A325886 (k=10).
Sequence in context: A369341 A368871 A120144 * A067452 A123944 A095046
KEYWORD
nonn
AUTHOR
Felix Fröhlich, Mar 23 2015
STATUS
approved